Process of removing carbon dioxide from gas streams using fuel cell



y 1970 J. GINER PROCESS OF REMOVING CARBON DIOXIDE FROM GAS STREAMS usmeFUQL' cm. Filed March so, 1967 :5 Sheets-Sheet 1 IMPURE AIR IN PURIFIEDAIR OUT KOH

KOH

F IG. 2

2 Q C T 54 INVENTOR JOSE GINER BYLflLfid/Z (I Made/son ATTORNEYS May 12,1970 J. GINER 3,511,712

PROCESS OF REMOVING CARBON DIOXIDE FROM GAS STREAMS USING FUEL CELLFiled March so, 1967 :5 Sheets-Sheet 2 H2/CO2 AIR KOH/KzCOs KOH I84 51,.C I89 KOH/K2CO3 INVENTOR JOSE GINER wit-im MQMM ATTORNEYS May 12,1970 IJ. GINER 351L712 PROCESS OF REMOV ING CARBON DIOXIDE FROM GAS STREAMSUSING FUEL CELL I Filed March 30, 1967 3 Sheets-Sheet 5 KOHCO; kK0H,CO3

I32 AIR Ilsa AIR SCRUBBER 2 FIG 4 I32 H2 \I 40 KOH KOH+K CO FromScrubber Hg e I94 .H+ OHZ o (-oH) K K CO q- I H" K K AMALGAM RegenermedAbsorber Solution INVENTOR F/G. 6 wubbe JOSE GINER WWII (QM/50mATTORNEYS streams by absorption,

United States Patent US. Cl. 13686 12 Claims ABSTRACT OF THE DISCLOSUREA process and system are provided for scrubbing CO from gas streams andregenerating the scrubbing medium. The scrubbing medium is an alkalinesolution, preferably of an alkali metal hydroxide. The regeneration iselfected 'by one or more regenerating fuel cells which utilize spentscrubber solution as an electrolyte. Hydroxyl ions are consumed at thecell anode, and produced at the cell cathode, and positive alkali metalions migrate from the anolyte to the catholyte to preserve theelectroneutrality of the cell. The pH of the anolyte solution is therebyreduced to about 9, and CO gas is evolved, regenerating the solution.The regenerating cell preferably contains a barrier spaced between theanode and cathode to prevent back diffusion of alkali metal hydroxidefrom the catholyte to the anolyte. The barrier can be a porousdiaphragm, but is preferably a cation permeable membrane.

This invention relates to the removal of carbon dioxide from gasstreams. More particularly, it relates to a process for removing carbondioxide (CO from gas which includes the periodic regeneration of thecarbon dioxide absorber to prepare it for additional absorption; and toregenerable carbon dioxide absorption systems used in this process.

It is greatly beneficial to remove carbon dioxide from many gas streams,such as from infiuent gas streams to fuel cells, from the air supplysystems of submarines, and the like.

A particularly important use for CO absorbers is in the purification ofinfiuent gas streams to fuel cells. Fuel cell electrolytes arefrequently materials which are reactive with carbon dioxide. Forexample, potassium hydroxide (KOH) and sodium hydroxide (NaOH) are oftenused as electrolytes, and both of these materials react avidly with COThus, if CO is allowed to enter the cell, it can react with theelectrolyte to form a precipitate which accumulates at the surfaces ofthe porous electrodes of the cell and reduces the efficiency andperformance of the cell.

The process and CO absorber system of this invention are particlul'arlyuseful in scrubbing either the oxidizing gas (generally, oxygen or air)supplied to the cathode of a fuel cell, the fuel gas (generally,hydrogen) supplied to the anode of a cell, or both.

Various methods and systems have been proposed in the prior art for theremoval of CO from gas streams. Absorbents of the soda-lime class havebeen used for this purpose, but these absorbents are not regenerable andmust be discarded when their absorptive capacity is exhausted. Certainregenerable CO absorbents have also previously been proposed. Exemplaryare molecular sieves and solutions of ethanol amine and other similarcompounds. Although these absorbents do have the advantage of beingregenerable, they also have undesirable shortcomings.

Molecular sieves absorb water vapor as well as CO 70 proved system forremoving C0 Because of the high ratio of water vapor to CO in air, theabsorptive sites of the molecular sieves become largely occupied bywater rather than CO and the CO absorption etficiency of the sieves isreduced substantially. The use of ethanol amine solutions and the likefor such absorption has also proved unsatisfactory, because the use ofsuch solutions requires the presence of tall countercurrent scrubbingtowers with associated pumps and other incidental space and weightconsuming equipment. These bulky equipment requirements are particularlyunsatisfactory in submarines and in small installations where fuel cellsmay be of particular interest.

Accordingly, to over come the foregoing disadvantages of prior artprocedures, it is a primary and general object of the present inventionto provide a new and improved process and system for removing CO fromgas streams.

Another object of this invention is to provide a new and improvedprocess and system for removing CO from gas streams with a regenerableCO absorber material.

A further object of this invention is to provide an improved process forremoving CO from gas streams by absorption, which process includesregeneration of the CO absorber.

Yet another broad object of this invention is to provide an improvedprocess and system for continuously removing CO from gas streams.

A still further object of this invention is to provide an improvedprocess and system for the continuous removal of CO from a gas stream inwhich a continuous source of CO absorption is provided by regenerationof a portion of the CO absorber while the remainder of the absorber isremoving CO from the influent stream.

Another object of this invention is to provide an imfromgases byabsorption, which system includes improved means for regenerating the COabsorber material.

Another object of this invention is to provide a process and system forthe removal of CO from a gas stream by absorption and for theelectrochemical regeneration of the CO absorber, which process andsystem utilize minimal energy in effecting the regeneration of the COabsorber.

Another object of this invention is to provide a process and system forthe removal of CO from a gas stream by absorption and for theelectrochemical regeneration of the CO absorber, which process andsystem utilize energy produced during the operation of at least one fuelcell to effect the electrochemical regeneration of the CO absorber.

Additional objects and advantages of this invention will be set forth inpart in the description that follows, and in part will be obvious fromthe description, or may be learned by practice of the invention, theobjects and advantages being realized and attained by means of themethods, processes, apparatus, and systems particularly pointed out inthe appended claims.

To achieve the foregoing objects, and in accordance with its purpose,this invention provides a process for removing CO from gas streams usinga strong base such as an alkali metal hydroxide as the absorbermaterial. The gas stream to be purified is brought into intimate contactwith an aqueous solution of this strong base, and a substantial portionof the CO in the gas stream is absorbed by the alkaline solution, andthereby removed from the stream.

The present process further provides for the regeneration of thealkalimetal hydroxide absorber solution to render it capable of furtherCO absorption, after its absorptive capacity has been partially orwholly exhausted: The process of this invention utilizes a fuel cellreaction and the energy generated in a fuel cell to either periodicallyor continuously regenerate the CO absorber solution and render itsuitable for further CO absorption.

This regeneration is achieved by introducing the alkaline absorbersolution, which contains carbonate produced by the absorption of CO intoa regenerating fuel cell as at least a portion of the fuel cellelectrolyte. Hydroxyl ionsare removed from a portion of the absorbersolution during operation of the fuel cell, while cO -containingcarbonate and bicarbonate ions remain in the solution. Concurrently withthe removal of hydroxyl ions from one portion of the solution, hydroxylions are added to a second portion of the solution and positive alkalimetal ions are transferred from the first portion to the second portionof the solution. This procedure reduces the pH of the first portion ofthe solution to a sufiicient extent that substantial amounts of gaseousCO are evolved from it. The second portion of the solution,vbecause ofthe accumulation of hydroxyl and alkali metal ions therein, isregenerated and becomes capable of absorbing additional C The presentinvention also provides a regenerable C0 absorber system for removing COfrom gas streams. This absorber system comprises absorbing means forpassing the gas stream'through a basic CO absorber solution, preferablyan alkali metal hydroxide solution, and regenerating means forperiodically regenerating the C0 absorber solution after its absorptivecapacity has been partially or wholly exhausted.

The regenerating means comprises at least one regenerating fuel cellhaving an anode and a cathode and utilizing the CO absorber solution asat least a portion of its electrolyte, said regenerating fuel cell beingprovided with retaining means to retain carbonate and bicarbonate ionscontaining ionically bound CO in the vicinity of its anode, and removalmeans to remove hydroxyl ions from the vicinity of the anode, therebyproducing a sufficient reduction of the pH of the electrolyte in thevicinity of the anode to cause the evolution of CO gas from theelectrolyte inthat vicinity. Hydroxy ions are added to another portionof the solution in the vicinity of the cell cathode to render thissecond portion of the solution suitable for further CO absorption.

The invention consists in the novel parts, constructioiis, arrangements,methods, processes, combinations and improvements shown and described.

The accompanying drawings, which are incorporated in and constitute apart of this specification, illustrate several embodiments of theinvention and, together with the description, serve to explain theprinciples of the invention.

0f the drawings:

FIG 1 is a diagrammatic representation of a regenerable' CO absorptionsystem which is suitable for the practice of this invention. This systemcontains a twocompartment regenerating fuel cell.

FIG. 2 is a diagrammatic representation of an expanded view of a portionof the anode of a regenerating fuel cell similar to that shown in FIG. 1except that the cell is divided into compartments by a diaphragmdirectly in contact with the anode.

' FIG. 3 is a diagrammatic representation of a two-compartmentregenerating fuel cell suitable for use in the continuous regenerationof a C0 absorber material in accordance with this invention.

FIG. 4- is a diagrammatic representation of a cascade of two-compartmentregenerating fuel cells, and is another embodiment of a regeneratingsystem suitable for use in the continuous regeneration of a C0 absorbermaterial in accordance with this invention.

FIG. 5 is a diagrammatic representation of another embodiment of aregenerating fuel cell suitable for the contmuous regeneration of C0absorber solution in accordance with this invention.

FIG. 6 is a diagramatic representation of a single compartmentregenerating fuel cell suitable for use in the CO scrubber system ofthis invention.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory but arenot restrictive of the invention. Reference will now be made in detailto the presently preferred embodiments of the invention, examples ofwhich are illustrated in the accompanying drawings.

As shown in FIG. 1, the scrubber system of this invention comprises a C0absorber or scrubber, generally 10, and a regenerator, generally 20.Impure gas, containing C0 is passed through a suitable absorber solutionin scrubber 10 prior to being used, i.e., prior its entry into a primaryfuel cell, prior to being returned to the atmosphere of a submarine or aspacecraft or the like. This absorber solution removes CO from theimpure gas by absorption.

As embodied and shown in FIG. 1, impure air enters a scrubber 10 throughimpure air inlet line Y12, and is passed through an absorber solutionwhich comprises a mixture of potassium hydroxide (KOH) and potassiumcarbonate (K CO This solution absorbs CO impurities in the air byconversion of at least a portion of the KOH to additional K CO Themechanism of this absorption reaction is shown by the followingequation:

The purified air, substantially free of CO exits scrubber 10 throughconduit 14 which directs it to where it is used, i.e., to an oxidant gaschamber adjacent the oxidant electrode of a primary fuel cell, or thelike.

In accordance with this invention means are provided for removing C0from a gas stream. The absorbing means of the CO scrubber system of thisinvention can comprise any suitable source of basic absorber solution,preferably an alkali metal hydroxide solution. Thus, for example,lithium hydroxide (LiOH), sodium hydroxide (NaOH), potassium hydroxide(KOH), and the like can be used. In accordance with a preferred form ofthis invention alkali metal carbonates are included in the absorbersolution along with the alkali metal hydroxides. These combinationabsorber solutions have been found to be particularly Well adapted toregeneration by the procedures of this invention.

Potassium hydroxide is a preferred alkali metal hydroxide scrubbingagent, and mixtures of potassium hydroxide and potassium carbonate havebeen found to have particularly high absorptive capacities for C0 Theabsorber solution is preferably richer in carbonate than in hydroxide,and can contain, for example, at least about I one gram equivalent offree alkali metal ion per liter of absorber solution. Exemplary ofspecific absorber solu tions which may be used in accordance with thisinvention are solutions of potassium hydroxide and potassium carbonatewhich contain about 1 to 2 gram equivalents of KOH per liter of absorbersolution and about 5 to 6 gram equivalents of K CO per liter of absorbersolution. Such scrubber solutions are effective, for example, to reduceand maintain the carbon dioxide content of a nonacidic fuel cellreactant gas such as air, oxygen, or hydrogen at less than two parts permillion.

In accordance with this invention, means are provided for periodicallyor continuously regenerating the absorber solution in the scrubbersystem, to render this absorber solution capable of additional COabsorption. As embodied and shown in FIG. 1, the regenerating meanscttmziprises a regenerating fuel cell indicated generally a As shownschematically in FIG. 1, regenerating fuel cell 20 comprises anode 22and cathode 24, which are electrtcally connected .by external loadcircuit 26- which allows the passage of electrons, generated at anode22, to cathode 24. Air or another suitable oxidant gas is supplied tocathode 24, while hydrogen or any other suitable fuel gas is-suppliedtoanode 22 in the manner shown schematicaly in FIG. 1. Regenerating fuelcell 20 contains a barrier 28 spaced between anode 22 and cathode 24.Barrier 28 divides the cell into an anolyte compartment indicatedgenerally as 30 and a catholyte compartment indicated generally as 32.

Both anode 22 and cathode 24 can be selected from conventional types ofelectrodes currently used in fuel cell technology. Thus, porous anodessuch as catalyzed screens or sintered powder anodes are suitable ashydrogen electrode 22 of the regenerating cell, and conventionalcathodes are normally suitable for use as oxygen electrode 24. Theoxygen electrodes should be of a type which will function efficientlywith free or circulating electrolytes, such as' catalyzed biporoussintered electrodes or screen electrodes with matrices.

In compartmented regenerating fuel cells of the type shown in FIG. 1,the spent absorbed solution, such as a mixture of KOH and K ispreferably supplied only to the anoltye compartment 30 of theregenerating fuel cell, as a portion of the total electrolyte of thecell. An alkali metal hydroxide solution, preferably KOH, is supplied tothe catholyte compatrtment 32 of the regenerating fuel cell, as theremaining portion of the electrolyte, through inlet line 41.

As shown in FIG. 1, the spent absorber solution is supplied to anolytecompartment 30 of regenerating fuel cell 20 from scrubber through inletline 42. The catholyte solution, such as KOH, is supplied to catholytecompartment 32 of regenerating fuel cell by any suitable means, such asfrom a catholyte reservoir (not shown) through conduit 41. The solutionsin the anolyte and catholyte compartments electrochemically connectanode 22 with cathode 24 by providing a medium for ion flow betweenthese electrodes.

The electrodes 22 and 24 of regenerating fuel cell 20 are electricallyconnected through external load circuit 26 which provides for thetransfer to cathode 24 of electrons generated at anode 22. Thus,external load circuit 26 provides the cathode 24 with continuous supplyof electrons necessary for the generation of hydroxyl (OH-) ions at thatelectrode, and at the same time affords a positive power output fromregenerating cell 20. This output contributes to the total power outputof the overall system which, includes scruber 10, and regenerating fuelcell 20, and can also include a primary fuel cell using the purifiedreactant gas supplied by scrubber 10.

The scrubber system of this invention also provides means fortransporting the CO -containing spent scrubber solution from scrubber 10to anolyte compartment 30 of regenerating fuel cell 20; and means forreturning the regenerated scrubber solution from catholyte compartment32 of regenerating fuel cell 20 to scrubber 10 for further COabsorption. These solution transport and return means are schematicallyindicated, respectively,

by arrows 42 and 45.

In operation of the scrubber system illustrated in FIG. 1, impure air ispassed through the absorber solution in scrubber 10, and then thepurified air is transported to the place of its use through conduit 14.

The spent scrubber solution is periodically or continuously transportedfrom scrubber 10 through regenerating fuel cell 20, and is returned toscrubber 10 through conduits 42 and 45, respectively. This transport isaccomplished by appropriate circulating pumps (not shown). The COabsorptive capacity of the scrubber solution is partially restoredduring its passage through regenerating cell 20.

In the operation of the regenerating cell, hydrogen ions and electronsare generated at anode 22, and the electrons pass through the externalload circuit 26 to cathode 24. These electrons are combined with theoxygen supplied to cathode 24 and the water present in the electrolyteat the cathode surface to generate hydroxyl ions at cathode 24.

The subreactions occurring at each electrode can be summarized asfollows:

ANODE REACTION (II) catalyst H: 20H- 2H20 2c CATI-IODE REACTION (III)catalyst The above reactions, occurring at the cell electrodes, dicatethe materials which must be used to construct the electrodes. Thus theelectrode material must be one which will promote the desired reactions,and particularly the anode must be constructed of a material which doesnot corrode significantly under the potential and pH conditions whichexist in its vicinity during the operation of the cell.Platinum-catalyzed nickel screen electrodes, and particularlyplatinum-catalyzed, gold-plated, nickel screen electrodes aresatisfactory for use in the regenerating fuel cells of this invention.

The over-all water-forming fuel cell reaction is exothermic, and isaccompanied by a release of suflicient energy to effect the reversereaction to that which occurs in the CO scrubber. In this reversereaction the potassium carbonate formed during CO absorption in thescrubber reacts with water, utilizing energy, to produce potassiumhydroxide and release carbon dioxide gas. This reaction can be indicatedas follows:

energy KzCOa H2O ZKOH C021 This CO evolution occurs in the vicinity ofthe anode of the regenerating fuel cell and removes C0 from the absorbersolution, thereby regenerating it for additional absorption.

As indicated schematically in FIG. 1, during the operation ofregenerating fuel cell 20 negative hydroxyl ions are produced at cathode24 of the cell according to Equation III while hydroxyl ions areconcurrently consumed at anode 22 according to Equation II. The positivepotassium ions in the electrolyte solution spontaneously migrate towardthe cathode of the cell to maintain the electroneutrality of bothcompartments, while the negatively charged ions in the solution migratetoward the anode of the cell. The following reactions occur at theanode:

These reactions result in the evolution of CO and hence the regenerationof the scrubber solution in the regenerating fuel cell. As OH" ions areconsumed at the cell anode, both of these equations are displaced to theright, continuing the CO evolution.

The formation of the bicarbonate ions by the reaction of Equation V, andthe subsequent evolution of carbon dioxode as shown by Equation VI are afunction of the pH of the anolyte solution. As operation of the cellcontinues, the KOH concentration in catholyte compartment increases anda corresponding decrease occurs in the KOH concentration of the anolytesolution due to the continuous production of hydroxyl ions at thecathode, the continuous consumption of hydroxyl ions at the anode, andthe continuous migration of the potassium or other alkali metal ionsthrough barrier 28 toward the cathode of the fuel cell.

This decrease in KOH concentration near the anode causes a decrease inthe pH of the anolyte (absorber) solution. When the pH of the anolyte isequal to or less than 12, the bicarbonate reaction of Equation V cantake place; and when, because of further consumption of hydroxyl ions atthe anode and the further potassium ion migration away from the vicinityof the anode, the pH of the anolyte solution reaches a value equal to orless than about 9, the evolution of substantial amounts of CO occurs inaccordance with the reaction of Equation VI.

The pH values at which these reactions occur are determined by the stateof the ionic equilibrium of the reactions.

The rate of evolution of C can be substantially increased by bubblingagas through the anolyte solution when the desired pH is reached. The gasused for this purpose can be air or an inert gas, preferably nitrogen,and this gas can be passed through the solution either in the anolytecompartment or after the solution is removed from that compartment.

Each of the regenerating fuel cells used in the CO scrubber system ofthis invention is provided with suitable means for the removal of thecarbon dioxode evolved during regeneration. Such removal means arediagrammatically illustrated by appropriate arrows in the accompanyingdrawings.

Referring again to FIG. 1, barrier 28 is preferably a cation permeablemembrane. Positive ions freelypass through such membranes, but themembranes are essentially impermeable to negative ions. Barrier 28 thusacts to retain negative hydroxide, carbonate and bicarbonate ions inanolyte compartment 30 but permits the steady and substantial migrationof positive alkali metal ions from anolyte compartment 30 to catholytecompartment 32 of the cell.

Cation permeable membrane 28 serves an additional function in preventingthe migration of hydroxyl ions generated at cathode 24 into anolytecompartment 30.

The primary function of cation permeable membrane or barrier 28 is toprevent or minimize back diffusion of KOH formed in catholytecompartment 32 into anolyte compartment 30. It can be seen from FIG. 1that for each hydrogen ion produced at anode 22, a hydroxyl ion isproduced at cathode 24. Simultaneously, there is a steady migration ofK+ ions through cation permeable membrane 28 toward cathode 24 (i.e., incatholyte compartment 32). Since the KOI-I formed in the catholytecompartment cannot pass through barrier 28, back diffusion of thepotassium into the anolyte compartment is prevented. It has been foundthat by the use of a cation permeable membrane in a regenerating fuelcell of the type shown in FIG. 1, more than 90% of the K+ ions in theanolyte solution can be transferred to the catholyte chamber of the fuelcell where they form KOH.

Referring once again to FIG. 1, as K+ ions migrate from anolyte chamber30 to catholyte chamber 32, the anolyte becomes progressively moredilute and the internal resistance of the cell increases. As thisdilution of the anolyte occurs, the effectiveness of barrier 28 inpreventing back diffusion of KOH into anolyte chamber 30 will alsodiminish because of the increasing concentration gradient across thebarrier. Both of these problems of increasing internal resistance andback diffusion can be alleviated by the addition of a supporting,neutral electrolyte to the anolyte solution. Exemplary of suchsupporting electrolytes are potassium fluoride (KF) and potassiumsulfate (K 80 In accordance with the present invention, the barrier usedto divide the regenerating fuel cell into anolyte and catholytecompartments can be a porous diaphragm rather than an ionic membrane ofthe type described above. A regenerating fuel cell using such a porousdiaphragm is illustrated in FIG. 5, which shows a continuous flowregenerating unit. This unit will be discussed fully hereinafter.

The porous diaphragms can be made of fuel cell grade asbestos films,porous rubber battery separators, porous nickel sheets, or Gelman W. A.Ion Exchange membranes (an extremely water permeable membrane which alsohas ion-exchange properties). Of course, any other suitable finelyporous diaphragm can be substituted for these specifically mentioneddiaphragms.

It will be appreciated from the above description that the presentinvention also encompases a process for removing CO from a gas stream.This process comprises passing the gas stream through a solution of astrongly basic material, such as an alkali metal hydroxide, to removesubstantial amounts of the CO by absorption in accordance with EquationI, above.

The absorber solution, containing absorbed CO is periodically orcontinuously regenerated in accordance with the process of thisinvention to render it capable of further CO absorption. Thisregeneration is effected by introducing the carbonate-rich absorbersolution into a regenerating fuel cell as at least a portion of the fuelcell electrolyte, and removing hydroxyl ions and alkali metal ions fromthe absorber solution (or a portion of it) during the operation of thefuel cell, while initially retaining in the absorber solution thecarbonate and bicarbonate ions containing absorbed C0 The pH of theabsorber solution, or a' portion of it, is thereby reduced to asufficient extent that substantial amounts of gaseous CO are evolvedfrom it.

The desired CO evolution occurs when the pH of the absorber solution isreduced to about 9 or less. Once the pH of the bulk anolyte is reducedbelow 9, carbon dioxide gas may bubble out of the anolyte solution asWell as being evolved into the excess hydrogen stream flowing throughthe hydrogen gas chamber.

If the cell is operated for a sufficient period, the following situationeventually prevails:

(1) Most of the potassium originally present in anolyte chamber 30appears as KOH in catholyte chamber 32;

(2) Most of the carbonate originally present in the anolyte has beenreduced to CO and vented from the cell;

(3) The anolyte solution has become largely deionized; I

(4) The cell voltage has diminished considerably.

At this point the anolyte solution chamber can be dis carded and thecatholyte solution, after suitable dilution or concentration, isavailable for use as essentially carbonate-free KOI-I solution. Thus,for example, one portion of the catholyte solution may be returned tothe scrubber, the remaining portion retained in the catholytecompartment for use in a subsequent regeneration cycle.

In practice, the lowest pH occurs in the electrolyte in closerelationship of the catalyzed sites within the anode.

The consumption of hydroxyl ions at these sites and hence the pH islowest there, since pH is directly proportional to the logarithm of thehydroxyl ion concentration. For this reason, evolution of C0 inpractice, occurs largely within anode 22.

In a preferred embodiment of this invention, as shown in FIG. 2, theanode of the regenerating fuel cell is provided with a barrier layer,which contacts the anode of its solution side, i.e., on the side of theanode which faces the electrolyte. This barrier aids in control of thecomposition of the electrolyte solution in the immediate vi cinity ofthe anode. It hinders indiscriminate mixing of the incoming bulkelectrolyte with the solution in the immediate vicinity of the anode,and aids in the establishment of a smooth pH gradient in the directionof the anode.

The anode barrier layer can consist of a thin layer of any suitableporous material, such as, for example, fuel cell grade asbestos film(preferably about 30- mils thick) or an anion exchange membrane.Alternative anode barrier layers can be provided by spraying, painting,or filtering such a layer directly onto the anode surface which facesthe electrolyte solution. Such layers can be made of spinel-Telfion orof a spinel-nickel mixture.

Since the region of lowest pH occurs within the pore structure of theanode, close to the gas-electrolyte interface, the use of such anodebarriers in no way restricts the escape of carbon dioxide gas into theexcess hydrogen gas stream exiting the regenerating fuel cell. By use ofthese anode barrier layers, however, it is possible to achieve improvedcomposition control of the solution reaching the immediate vicinity ofthe anode of the regenerating fuel of the anode electrode) can beflushed away with excess fuel gas (e.g., H The additional fuel gasnecessary to flush away the ably a thin porous asbestos film, any of thealternative types of anode barrier layers described above can besubstituted for such asbestos film.

It should be noted that the operation of the system of this inventioncan be carried out without a diaphragm of any type in some cases,particularly where the electrolyte has a low OH- concentration (i.e.,less than about moles/liter). Such operation is possible because theporous surface of the anode itself assumes somewhat the character of abarrier, controlling the composition of the electrolyte within theanode, hindering indiscriminate mixing of the solution in the anode withincoming bulk electrolyte, and aiding the establishment of a smooth pHgradient in thedirection of the anode.

Operation of the regenerative cell without the use of an added barrierlayer is facilitated by the use of suitable anode polarization so thatthe electrolyte in the gas side (surrounding the activated portion ofthe CO in such systems is compensated by the simplification of cellconstruction and the reduction in the internal resistance of the cellmade possible by the elimination of the barrier.

Referring to FIG. 2, regardless of whether barrier 54 is an added porousdiaphragm or the like or is merely the inherent barrier afforded by theporous surface of the electrode, the area of lowest pH occurs at thecatalytic sites of the anode where dissolved hydrogen is ionized andhydroxyl ions consumed, and therefore the primary CO evolution occurswithin the pores of anode 52. The CO gas there formed can be flushedfrom the regenerating fuel cell with excess hydrogen supplied by fuelsupply means 60. The exiting fuel stream indicated schematically in FIG.2 thus contains the CO evolved in the regenerating cell. It alsocontains excess product water removed from the cell in the excess fuelgas stream. The excess H gas in this stream can be recovered byseparation from the CO and water vapor with an appropriately selectivemembrane.

Removal of CO in the excess hydrogen stream in this manner lends itselfparticularly well to use in regeneration of Co -scrubbers in nuclearsubmarines where H; gas is normally dumped into the sea. Using thissystem the excess H gas could be used to remove the CO evolved in thescrubber from the ship.

The regenerating cell shown in FIG. 1 performs a batchtype regeneration.If continuous scrubbing is to be afforded in the scrubber step of theprocess and system of this invention, alternate sources of scrubbing orabsorbing solution must be provided in order to effectively utilize sucha batch-type regeneration system. For example, referring to theregeneration system illustrated in FIG. 1, a first batch of absorbersolution can be used to scrub CO from the influent gas to the primaryfuel cell until its absorptive capacity is expended. The spent absorbersolution is then removed from scrubber 10 and passed to regeneratingfuel cell 20 for regeneration. Meanwhile, if CO scrubbing of the gasstream is to continue, either a second source of absorbing solution mustbe supplied to scrubber 10, or an alternate scrubber must be provided.Subsequently, the first batch or regenerated solution can be returned toscrubber 10 for further C0 absorption; and the spent second batch ofscrubber solution can be transported to fuel cell 20 for regeneration.

It is possible to dispense with the second scrubbing chamber if theregenerating cell is designed for dual purpose operation. In such asystem the influent gas to the primary fuel cell is passed directlythrough and brought into intimate contact with a supply of absorbersolution in the regenerating fuel cell. When the absorptive capacity ofthis solution is expended, the influent gas is diverted to analternative source of absorber solution, and the regenerating fuel cellis activated and operated inthe manner described above to regenerate theabsorber solution and render it capable to additional absorption.

It is highly desirable in accordance with this invention to provide acontinuous source of CO absorption. To achieve this result, when theabove-described batch-type regenerating systems are used, it isgenerally desirable to provide several sources of scrubbing or absorbingsolution and preferably also more than one regenerating fuel cell foralternating use.

An alternative procedure for providing continuous scrubbing, andcontinuous regeneration of the absorber solution can be achievedutilizing a compartmented regenerating fuel cell of the type illustratedin FIG. 1. Using this system, the influent gas to the primary fuel cellis first passed through the electrolyte in anolyte compartment 30 of theregenerating fuel cell 20 for CO absorption, and then through theelectrolyte of catholyte compartment 32 while the electrolyte in anolytecompartment 30 of that cell is being regenated in the manner describedabove. When the regeneration of the anolyte solution is completed, theinfluent gas to the primary fuel cell is once again directed throughanolyte comparement 30 for additional CO absorption, while the cathoyltesolution is being regenerated.

Regeneration of the catholyte solution is accomplished by reversing theoperation of the regenerating fuel cell 20, converting the originalcathode 24 to an anode. By periodically reversing the operation of thecell with appropriate electrode reversal means and simultaneouslydiverting the flow of Co -containing influent gas through the respectivechambers of regenerating fuel cell 20 with appropriate control means,this cell can provide continuous absorbing means and regenerating meansfor the CO scrubber system of this invention.

Thus it can be seen that the CO absorption of the present invention canbe accomplished either in the regenerating fuel cell itself or in ascrubbing chamber which is distinct from but operatively connected withthe regenerating fuel cell. For continuous scrubbing action, the COrich, spent absorber solution can be passed from the srubbing chamber tothe regenerator and a new or regenerated absorbing solution used in thescrubbing chamber; or two scrubbing chambers can be used alternatively;or cell operation can be periodically reversed with scrubbing carriedout alternatively in each of the compartments of a compartmentedregenerating cell of type illustrated in FIG. 1.

'Another alternative continuous operating procedure is to feed spentscrubber solution to the anolyte compartment 30 at a slow, controlledrate to maintain the pH in that compartment at about 9. Simultaneously,KOH solution is slowly Withdrawn from the cathode compartment andreturned to the scrubber for further CO absorption. The feed andwithdrawal rates would be matched to maintain the solution in thescrubber at a constant volume and composition.

Additional regenerating fuel cells coming within the purview of thisinvention are illustrated in FIGS. 3-6. FIG. 3 illustratesdiagrammatically a continuous action regenerating fuel cell, generallyan anode 102 and a cathode 104, and is provided with a barrier 106spaced between its anode and its cathode and dividing the cell into twocompartments. Barrier 106 is preferably a cation permeable membranewhich acts to retain carbonate and bicarbonate ions (containing absorbedCO in anolyte compartment 108 of the regen- 100. The cell comprises l 1erating cell, and allows substantial amounts of positive alkali metalions (such as K+ ions) to pass through it and out of anolyte compartment108 into catholyte compartment 110.

Regenerating fuel cell 100 illustrated in FIG. 3 functions chemically inthe same manner as fuel cell 20-, illustrated in FIG. 1. Thus, inoperation of fuel cell 100, negatively charged hydroxyl ions in theanolyte compartment 108 are consumed by reaction with hydrogen at anode102 (according to reaction '11), and positively charged potassium ionsmigrate from anolyte compartment 108 to catholyte compartment 110,thereby reducing the pH of the electrolyte solution in the anolytecompartr'nent. The difference in the operation of continuousregenerating cell 100 is that spent absorber solution is continuouslypassed into the cell at one end of its anolyte compartment 108 bysuitable transport means, such as conduit means 112, and is thencontinuously passed through anolyte compartment 108 to the other end ofthat compartment (indicated generally at 114).

In operation of the cell, as described above, hydroxyl ions arecontinuously consumed at anode 102 and potassium ions continuouslymigrate out of anolyte compartment 108 during the passage of thesolution through that compartment, so that the pH of the anolytesolution is continuously reduced during its passage through the anolytecompartment.

When the anolyte solution reaches a pH of about 9, little or no KOHremains in anolyte compartment 108, and the anolyte solution isessentially an aqueous solution of K CO and KHCO Because of the thermaldisassociation of the bicarbonate radical in this solution, there is afinite pressure of CO above the solution which increases withtemperature. If the regenerating fuel cell is operated at a suflicientlyhigh temperature, such as above about 50 C., a certain amount of CO gasis liberated within the cell itself in the form of gas bubbles in theelectrolyte.

In the regenerating fuel cell system illustrated in FIG. 3 this thermaldisassociation eflect is utilized to enhance the overall rate of COevolution from the anolyte solution. The carbonate-rich solution beingregenerated is cycled from anolyte compartment 108 of regenerating cell100 through an external heated chamber 116, Where the solution is heatedto a temperature above 50 C. and sparged with an inert gas stream.Although any inert gas can be used for this sparging, nitrogen ispreferred. Air is also inert enough for this usage and would remove moreCO than it would add. Thus, air because of its ready availability andlow cost is also a desirable sparging medium.

The system of FIG. 3 achieves highly efiicient CO removal, and by propercontrol of the temperature in the purging chamber and the flow rate ofthe inert gas, this system also efiiciently removes by-product waterfrom the anolyte solution along with the C The regenerated solutionleaving heating and sparging chamber 116 passes down through catholytecompartment 110 of the cell, where it receives the potassium ions thathave migrated through membrane 106 from anolyte compar'tment 108. Whenthe regenerated absorber solution has completed its passage throughcatholyte chamber 110, it is returned to the scrubber (not shown) foradditional CO absorption.

It will be readily apparent to those skilled in the art that theregenerating system illustrated in FIG. 3 can continuously receive spentabsorber solution from a scrubher and simultaneously return regeneratedabsorber solution to the scrubber. Alternatively the continuousregeneration achieved with the system of FIG. 3 can operate inconjunction with a plurality of scrubbers, receiving spent absorbersolution from one scrubber and returning regenerated solution toanother.

Another embodiment ofa continuous regenerating unit for the scrubbersystem of this invention is illustrated in FIG. 4. This regeneratingsystem, which operates in con junction with scrubber of FIG. 4,comprises a cascade of fuel cells connected to each other in a mannersuitable to provide for the flow of electrolyte from one cell to othersof the cascade.

The electrolyte (which is the spent absorber solution from scrubber 120)is transported from scrubber 120 to anolyte compartment 122 of theinitial cell in the cascade through inlet line 149, and then issuccessively transported through anolyte compartments 124, 126, 128, andof the remaining cells of the cascade. The pH of the electrolyte(absorber) solution is continuously reduced during its passage througheach of these anolyte compartments, because of the consumption of OHions at the anode of each cell by combination of these ions withhydrogen ions generated at the anodes, and the simultaneous migration ofpotassium ions from each of these compartments through barriers 132 ofeach cell to compensate for the OH- ions generated at the cathodes ofthe cells.

The pH of the absorber solution is sufliciently reduced that CO isevolved from anolyte compartment 130 of the last cell in the cascade. Ifdesired, the absorber solution being regenerated can be cycled fromanolyte compartment 130 through a heating and sparging chamber similarto that utilized with the regenerating fuel cell illustrated in FIG. 3.The regenerated solution is then cycled through catholyte chamber of thelast cell in the cascade and subsequently through catholyte chambers142, 144, 146, and 148 of the remaining cells in the cascade.

The alkalinity of the solution is increased in its passage through eachof these respective catholyte chambers by the migration of additional K+ions from the subsequently cycled absorber solution in the anolytechambers of the respective fuel cells of the cascade. The solutionexiting catholyte chamber 148 of the first cell in the cascade 1s acompletely regenerated absorber solution which is continuously returnedto scrubber 120 through conduit 150 for additional absorption.

The use of a cascade of cells of the type illustrated in FIG. 4 providesseveral incident benefits. The most important is the increasedefliciency of operation achieved. When a single regenerating fuel cellof the type indicated in FIG. 3 is used, the internal'resistance of thecell increases as regeneration proceeds. Fur'ther, the voltage developedby the cell decreases as the pH diiferential between the anolyte andcatholyte increases. The increase in internal resistance and drop involtage act together to reduce the cellcurrent and thereby slow down theregeneration process.

By using a cascade of cells of the type shown in FIG. 4, connectedelectrically in series, the overall voltage cificiency of the system isincreased. This increase in efi'lciency is possible because the pH ofthe solution in anolyte compartment 122 of the first cell in the cascadeis virtually the same as the pH of catholyte chamber 148 of .the firstcell of the cascade (pHl4).

It will be readily apparent to those skilled in the art that the cascadecan contain any desired number of fuel cells. As more cells are includedin the cascade, overall performance will more nearly approachtheoretical. The only limitation on the number of cells which can beincluded in the cascade is dictated by the added complication of theinclusion of additional cells.

The diminishing volume of the regenerating fuel cells in the cascadeshown in FIG. 4 is designed to accommodate water removal from theanolyte compartment of each cell as the concentration of the electrolytebecomes more dilute because of the migration of K+ ions from the anolytecompartment to the catholyte compartment of each cell. correspondingly,as the solution advances from catholyte compartment 140 of the last cellin the cascade through the catholyte compartment of each succeedingcell, the size of that compartment is increased to allow water As thesolution used in the scrubber systems oxidant gas, such as air (showndiagrammatically in FIG.

). Electrons formed at anode 182 are transported to cathode 184 by asuitable external load circuit (not shown). The electrodes areelectrochemically connected by means of an electrolyte disposed betweenand in contact with them.

Regenerating fuel cell 180 contains a barrier 186 spaced between itsanode 182 and its cathode 184. Barrier 186 divides the regenerating cellinto an anolyte compartment,

' indicated generally as 188, and a catholyte compartment indicatedgenerally as 189. This barrier, like the cation permeable membrane usedas barrier 28 in FIG. 1, acts primarily to prevent back dilfusion of KOHfrom catholyte compartment 189 to anolyte compartment 188. Barrier 186,however, is a. porous diaphragm rather than a cation permeable membrane.Although the use of a regular diaphragm material is accompanied by alower mass transfer efficiency, this in some instances, may be more thancompensated for by the higher conductivity, lower cost and highercorrosion resistance of the regular diaphragm.

In the regenerating fuel cell illustrated in FIG. 5, the

I spent absorber solution is passed through the cell at a sufficientrate to prevent or at least inhibit back diffusion of KOH from catholytecompartment 189 to anolyte compartment 188. Thus the steady removal ofhydroxyl ions at anode 182 of the cell sufficiently reduces the pH ofthe expended electrolyte solution in anolyte compartment .188 to causeCO evolution from the anolyte compartment.

Regenerating fuel cell 180 of FIG. 5 is horizontally oriented. Suchorientation is preferred in cells which utilize porous diaphragmbarriers to define their anolyte and catholyte compartments. The primaryadvantage of such horizontal orientation is that the hydrostaticpressure head over the surface of the electrodes is small and uniform incomparison to vertically disposed cells, in which the hydrostaticpressure on the electrode faces increases from the top of the cell tothe bottom.

In the operation of horizontally-oriented, continuous, regenerating fuelcell .180 of FIG. 5, spent electrolyte solution from the scrubber (notshown) enters the fuel cell in anolyte compartment 188 as the cellelectrolyte. 'passes through the cell, OH- ions are consumed at anode182 and produced at cathode 184, and K ions migrate through porousdiaphragm 186 into catholyte compartment 189 to maintain theelectroneutrality of the cell. Of course, since diaphragm 186 is notionically selective, its purpose is only to minimize convection anddiffusion mixing in the electrolyte. However, for every 100 OH ionsconsumed at anode 182, 100 OH- are produced at cathode 184, about 50 K+ions leave the anolyte through porous diaphragm 186, and only about 50OH- ions enter the anolyte through diaphragm 186. Because of thisdisproportionate transfer of OH ions to the catholyte, a regeneratedelectrolyte solution of substantially reduced CO content can be removedfrom catholyte compartment 189 at the downstream end of the regeneratingfuel cell 180.

An additional embodiment of the regenerating fuel cell of this inventionis illustrated in FIG. 6. As there shown, regenerating fuel cell 190comprises a single chamber containing reversible electrode 192 andamalgam electrode 194. As in the regenerating fuel cells describedabove, the spent scrubber solution is introduced into regenerating fuelcell as the cell electrolyte, and is disposed between and in contactwith reversible electrode 192 and amalgam electrode 194. Electrode 192is suitably connected to alternate sources of hydrogen and oxygen, or toalternate sources of any other suitable fuel and oxidant gases.

Electrodes 192 and 194 are connected through external load circuit 196which allows electrons to be transferred between the electrodes of thecell.

As shown in FIG. 6, the regeneration of the electrolyte (absorber)solution is achieved by supplying hydrogen or another fuel gas toreversible electrode 192, which, operating as a standard anode, produceshydrogen ions and generates electrons which flow through external loadcircuit 196 to amalgam electrode 194. Amalgam electrode 194 utilizesthis electrical energy to remove from the solution potassium (K'') ionswhich are attracted to the vicinity of the negative amalgam electrodeduring operation of the cell. This removal of potassium ions from thebulk electrolyte solution eventually reduces its pH to about 9 or less,causing the evolution of CO gas from the electrolyte solution, andthereby regenerating the solution and rendering it suitable for additionCO absorption.

When the desired CO evolution is completed, the direction of electronflow through the external load circuit is reversed, so that amalgamelectrode 194 releases K+ ions into the bulk electrolyte solution,thereby further increasing its alkalinity and CO absorptive capacity.Reversible electrode 192, meanwhile, is connected to a source of oxygengas and produces 0H- ions. The reverse phase of this reaction isschematically shown in parenthetical form in FIG. 6.

By connecting two equal regenerating fuel cells of the type shown inFIG. 6 in series, and operating them in such a manner that one celldecreases the KOH content of its bulk electrolyte, thereby effecting COremoval, while the second cell in the series increases the KOH of itsbulk electrolyte, the overall amount of energy used by the regeneratingcells can be kept to a minimum.

The present invention provides a new and improved process and system forscrubbing CO from impure gas streams. The process and system of theinvention provide for both the scrubbing of the CO from such gases, andfor .either periodic or continuous regeneration of the scrubber solutionused for this purpose.

In accordance with this invention, such regeneration is carried outusing one or more regenerating fuel cells. The use of such regeneratingfuel cells allows efiicient scrubbing of the CO -containing gases, andpractical and eflicient regeneration of the scrubber solutions.

The regenerating fuel cells used in accordance with this invention havebeen primarily described as operating on hydrogen and air as theirreactant gases, and producing hydrogen ions (H+) at the cell anode andhydroxyl ions (OH-) at the cell cathode in accordance with Equations inand III above. It is to be understood, however, that any suitable fueland oxidant gases can be used in the regenerating fuel cells utilized inaccordance with this invention. Thus the regenerating fuel cells canoperate on any appropriate electrode reactions, which, in addition tothose described, include the following reactions at the anode 15 CATHODEREACTIONS (If a. redox system is added to the electrolyte) Any of theseelectrode reactions can supply and consume the OH- ions necessary forthe C generating reactions which are produced in the regenerating fuelcell in accordance with this invention. Any pair of these electrodereactions can thus be selected to best achieve a combination ofsimplicity and energy economy. Generally, the lowest energy requirementsare achievable with the hydrogen-oxygen fuel cell system illustrated byEquations ill and III.

Certain embodiments of the regenerating fuel cells utilized inaccordance with this invention, for example those illustrated in FIGS. 1and 3-5 utilize compartmented regenerating fuel cells, which are dividedinto anolyte and catholyte compartments by a barrier disposed betweenthe anode and cathode of the cell. The illustrated cells all containonly two compartments. It is to be understood, how

vide the regenerating cell into three compartments, and

to cause C0 evolution between the two membranes or barriers, and therebyrelieve the anode of its C0 evolving duties. The location of stillanother barrier between the anion permeable membrane described above andthe cathode of the multi-compartment fuel cell could provide a fourthcompartment of a cell suitable for both CO absorption andabsorber'regeneration. The raw, CO -containing air would be introducedinto this fourth compartment and the scrubbed air removed from it. Thisfourth compartment would thus serve to prevent the stream of purifiedair leaving the cell from interfering with the operation of the cellcathode.

While scrubbing and regenerating fuel cells containing such additionalcompartments are within the contemplation of the broad process andsystem of this invention, it is not believed that the additionalcomplexity introduced into the cell structure by such additionalbarriers is generally warranted by the increase in operating efliciencyachieved by their use.

For a clearer understanding of the invention, specific examples of itare set forth below. These examples are merely illustrative and are notto be understood as limiting the scope and underlying principles of theinvention in any way.

Example 1 A fuel cell having platinum-catalyzed, wet-proofed,

screen electrodes of 40 cm. geometric surface area placed 1 cm. apart isdivided into two chambers by a cation permeable membrane situated midwaybetween the two electrodes. Hydrogen is fed to one of the electrodes(the anode) and oxygen to the other electrode (the cathode). An anolytesolution having a volume of 150 cc. and initially containing 1 g.equivalent of KOH per liter and 4 g.

equivalents of K C0 per liter is continuously circulated at 130 cc./min.from a reservoir through the anode cham ber of the cell. A catholytesolution having a volume of 2000 cc. and and containing initially 1 g.equivalent of KOH per liter and 0.02 g. equivalents of K CO per liter iscontinuously circulated at 130 cc./min. from a reservoir I through thecathode chamber of the cell. The cell is op- The total volume of thecatholyte after this period of operation is 2000 cc. containing 1.39 g.equivalents of KOH per liter and 0.025 g. equivalents of K CO per liter.More than 12 g. of CO has been evolved from the cell during the 15 hourperiod of operation and over 90% of this evolved CO has been carried offby the excess hydrogen stream passing through the fuel gas chamberadjacent the anode.

Example 2 The procedure of Example 1 is repeated using an anolytesolution which has a total volume of 150 cc. and contains 4 g.equivalents of K 00 per liter, and a catholyte solution which has atotal volume of 1500 cc. and contains 1 g. equivalent KOH per liter.Hydrogen is fed to the anode and air to the cathode in the manner ofExample l. The pH of the anolyte solution drops from 12 to 9 over aperiod of 4% hours and remains at about 9 for an additional 6% hours.

Carbon dioxide is detected in the excess hydrogen stream leaving theanode gas chamber after one hour of operation, and the rate of C0evolution reaches a maxi- Example 3 The procedure of Example 2 isrepeated in this example With the addition of a sparging chamber to theanolyte circulation loop. The sparging chamber is situated near theanolyte outlet from "the cell and provides a slow flow of nitrogenthrough the anolyte solution leaving the chamber. After a total of 10hours of cell operation, chemical analysis of the anolyte and catholytesolutions shows that 79% of the CO originally present as carbonate inthe anolyte solution has been evolved from the cell. The distribution ofthe evolved C0 is determined by passing the excess hydrogen flow and theexit N purge through separate soda lime tubes. The gain in weight of thesoda lime tubes reveals that approximately 0.4 g. equivalents of CO havebeen evolved in the excess hydrogen flow and about 0.1 g. equivalents ofCO have been evolved in the N purge.

Example 4 v- A fuel cell having platinum-catalyzed, wet-proofed,

' screen electrodes with 40 cm. of-geometric surface area is assembledwith an electrode separation of 0.5 cm. The two electrodes are connectedexternally by a low resistance circuit. A 10 mil thick sheet of asbestospaper is placed against the anode, on its electrolyte side, and retainedthereby a tantatlum screen. One hundred fifty ml. of 7 N K CO iscontinuously recirculated through the cell while hydrogen is fed to theanode and air to the cathode. The cell is operated at 50 C.

The hydrogen exhaust stream leaving the anode gas chamber is dried andthe CO which it contained is collected quantitatively by adsorption insoda lime tubes, which are weighed periodically. K CO is progressivelyconverted to KOH during the cell operation, with the rate of evolutionof CO diminishing as the pH of the electrolyte increases.

Typical values for the rate of CO evolution occurring at variousspecific electrolyte compositions are shown in Table 1 as follows:

TABLE 1 Composition of Electrolyte, Equivalents Equivalents per 001Evolved Liter er Hour per Liter of Cell K200; KOH Volume 1 7 Example 5The procedure. of Example 4 is repeated with an additional 20 mil layerof asbestos paper attached to the electrolyte side of the anode. Therates of CO evolution corresponding to specific electrolyte compositionsare shown in Table 2.

TABLE 2 Composition of Electrolyte, Equivalents Equivalents per EvolvedLiter per Hour per Liter of Cell K100 KOH Volume 6. 0. 5 l. 9 6. 0 1.0 1. 7 5. 5 1. 5 l. 5 5. 0 2. 0 l. 3 4. 5 2. 5 1. 1

This invention in its broader aspects is not limited to the specificdetails shown and described, but departures may be made from suchdetails within the scope of the accompanying claims without departingfrom the principles of the invention and without sacrificing its chiefadvantages.

' What is claimed is:

1. A process for removing carbon dioxide from a gas stream with aregenerable carbon dioxide absorber system which generates an electricalenergy, said process comprising the steps of:

(a) passing the gas stream through a carbon dioxide absorber systemcomprising an aqueous solution of an alkali metal hydroxide, whereby thecarbon dioxide content of said gas stream is substantially reduced byabsorption of carbon dioxide in said aqueous solution, said absorptionbeing effected by the formation of alkali metal carbonate in saidabsorber solution; and

(b) periodically or continuously regenerating said alkali metalhydroxide solution to render it suitable for additional carbon dioxideabsorption, said regeneration being effected by: passing the alkalimetal carbonate-rich aqueous absorber solution to the vicinity of theanode of a regenerating fuel cell as at least a portion of the fuel cellelectrolyte, the fuel cell operating by the consumption of an oxidantand a fuel to generate hydrogen ions and consume hydroxyl ions at itsanode, to generate hydroxyl ions at its cathode, and to generateelectrical energy; allowing the alkali metal ions in said solution tomigrate to the vicinity of the cathode of the fuel cell while retainingions containing ionically bound carbon dioxide in the vicinity of theanode, said consumption of hydroxyl ions at the anode, production ofhydroxyl ions at the cathode and migration of alkali metal ions to thevicinity of the cathode reducing the pH of the electrolyte in thevicinity of the anode to a suflicient extent that substantial amounts ofgaseous CO are evolved and simultaneously increasing the pH of theelectrolyte in the vicinity of the cathode to a sufficient extent torender it capable of absorbing substantial amounts of carbon dioxide.

2. The process of claim 1, in which said absorber solution comprisespotassium hydroxide.

3. The process of claim 1, in which tron comprises a mixture ofpotassium carbonate.

4. The process of claim 3 in which said absorber solution contains about1 to 2 gram equivalents of potassium hydroxide per liter of solution andabout 5 to 6 gram equivalents of potassium carbonate per liter ofsolution.

5. The process of claim 1, in which a supporting, substantially neutralelectrolyte is added to the electrolyte said absorber solupotassiumhydroxide and in the vicinity of the anode of the regenerating fuel cellduring the migration of potassium ions to the v cinity of the cathode ofsaid cell to prevent undue dilutlon of the electrolyte surrounding thecell anode and an accompanying increase in the internal resistance ofthe cell.

6. The process of claim 5, in which the supporting electrolyte ispotassium fluoride or potassium sulfate.

7. The process of claim 1, in which the pH of the electrolyte in thevicinity of the anode is reduced to about 9 or less, and the electrolyteis heated to a temperature of at least about 50 C. and sparged with aninert gas to remove carbon dioxide therefrom.

8. The process of claim 7 in which the electrolyte in the vicinity ofthe anode is withdrawn from the regenerating fuel cell when it reachesabout pH 9, and is passed to an external heating chamber where it isheated to at least 50 C. and sparged with an inert gas to purge CO; fromsaid solution.

9. The process of claim 1 in which said absorber system comprises anaqueous absorber solution containing a mixture of alkali metal hydroxideand alkali metal carbonate.

10. The process of claim 9 in which said absorber solution is richer incarbonate than it is in hydroxide.

11. The process of claim 1 in which the alkali metal hydroxide absorbersolution is maintained in the vicinity of the anode of the regeneratingfuel cell and the carbon dioxide-containing gas stream is passed throughsaid solution in said cell to achieve the desired carbon dioxideabsorption; said cell being activated periodically for regeneration ofsaid solution, and said gas stream being diverted to another source ofabsorber solution during said regeneration.

12. A process for operating a primary fuel cell utilizing an influentfuel gas stream and an influent oxidant gas stream to generateelectrical energy, said process including the steps of:

(a) removing carbon dioxide from at least one of said infiuent gasstreams before said stream is introduced into the primary fuel-cell bypassing said stream through a carbon dioxide absorber system comprisingan aqueous solution of an alkali metal hydroxide, whereby the carbondioxide content of said gas stream is substantially reduced byabsorption of carbon dioxide in said aqueous solution, said absorptionbeing elfected bythe formation of alkali metal carbonate in saidabsorber solution;

(b) passing the purified influent gas stream to the primary fuel cell;and

(c) periodically or continuously regenerating said alkali metalhydroxide solution to render it suitable for additional carbon dioxideabsorption, said regeneration being effected by: passing the alkalimetal carbonate-rich aqueous absorber solution to the vicinity of theanode of a regenerating fuel cell as at least a portion of the fuel cellelectrolyte, the fuel cell operating by the consumption of an oxidantand a fuel to generate hydrogen ions and consume hydroxyl ions at itsanode, to generate hydroxyl ions at its cathode, and to generateelectrical energy; allowing the alkali metal ions in said solution tomigrate to the vicinity of the cathode of the fuel cell while retainingions containing ionically bound carbon dioxide in the vicinity of theanode, said consumption of hydroxyl ions at the anode, production ofhydroxyl ions at the cathode, and migration of alkali metal ions to thevicinity of the cathode reducing the pH of the electrolyte in thevicinity of the anode to a suflicient extent that substantial amounts ofgaseous CO are evolved and simultaneously increasing the pH of theelectrolyte in the vicinity of the cathode to a sufficient extent torender it capable of absorbing substantial amounts of carbon dioxide.

(References on following page) 1 9 References Cited UNITED STATESPATENTS 3/1942 Berl 136--86 4/1963 Taylor- 136-86 X 11/1965 Worshaml3686 X 5 5/1967 Palmer 136-86 20- 3,411,951 11/1968 Gelting 136-863,196,092 7/1965 Beer 204 130 AL'LEN B. CURTIS, Primary Examiner U.s.c1.X.R.

